1. Field of the Invention
The present invention relates to a dynamic damper having a generally cylindrical shape, and installed on a hollow or a solid rod member which is subject to oscillation and which is a member of a vibration transmitting system such as shafts, arms, or conduits used in various devices, for reducing or absorbing vibrations of the oscillating rod member, and further relates to a method of producing the dynamic damper.
2. Description of the Related Art
Various kinds of rod members such as shafts or arms functioning as a power transmitting members and such as conduit or pipes serving as a fluid passage generally tend to oscillate or vibrate and consequently resonate due to an external oscillating force. Further, the rod member undesirably transmits a vibration excited therein to other components of a device in which the rod member is used. As a method to cope with these problems, a dynamic damper is attached to the rod member for preventing the resonance of the rod member and the transmission of the excited vibration of the rod member to the other components.
Examples of such a dynamic damper are disclosed in JP-A-2-190641, JP-B-6-037915, and JP-A-10-132027, wherein the dynamic damper has a mass member having a generally cylindrical configuration and an elastic support member secured to the mass member. The disclosed dynamic damper is installed onto an oscillating rod member and secured thereto at the elastic support member so that the mass member is elastically supported on the oscillating rod member via the elastic support member. The dynamic damper installed on the oscillating rod member as described above constitutes a secondary vibration system in which the mass member serves as a mass and the elastic support member serves as a spring, with respect to the oscillating rod member as a primary vibration system. The thus constructed dynamic damper is properly tuned so that the dynamic damper is capable of exhibiting effective damping characteristics with respect to a torsional or circumferential vibration as well as an axial and a radial vibration of the rod member. Since the mass member has the cylindrical shape, the mass member of the dynamic damper is not released from the rod member, even if the elastic support member is undesirably broken. In other words, the dynamic damper having the cylindrical mass member has a so-called xe2x80x9cfail-safexe2x80x9d structure. For the above, the dynamic damper is considered to be installed on a drive shaft of an automotive vehicle for absorbing or reducing vibrations thereof, for example.
The conventional dynamic damper preferably comprises the mass member consisting of a cylindrical mass formed of a metallic material such as carbon steel, which is available at a relatively low cost and which has a relatively large mass and the elastic support member which is bonded to the cylindrical metallic mass member in the process of vulcanization of a rubber material for forming the elastic support member, with the mass coated by an adhesive material. The cylindrical metallic mass may be formed by casting a metallic material, by cutting a metallic piping member in a suitable length or by roll molding a metallic plate to form a cylindrical member.
However, the metallic mass prepared by casting has a low dimensional accuracy, resulting in difficulty in providing a desired mass of the metallic mass with high accuracy. Further, the metallic mass formed by casting suffers from a problem of difficulty in providing a desired high-specific gravity thereof and a problem of cumbersome manufacturing processes and post-treatments. On the other hand, the metallic mass formed of the metallic piping member by cutting in the suitable axial length, or the metallic mass formed of the metallic plate by pressing, e.g., by roll molding, may be produced with ease and with high-dimensional accuracy. However, such a metallic mass undesirably requires a significantly high-manufacturing cost due to the expensive piping member or undesirably required huge and expensive dies for the press.
In order to reduce the manufacturing cost of the dynamic damper, there is proposed to omit an adhesion treatment e.g., applying the adhesive between the elastic support member and the metallic mass. To this end, the dynamic damper may be modified to further comprise a rubber layer which is adapted to cover a substantially entire area of the outer surface of the metallic mass and integrally formed with the elastic support member, so that the elastic support member is fastened to the metallic mass without the above-indicated adhesion treatment. The thus constructed dynamic damper however, cannot provide resilient bonding strength between the elastic support member and the metallic mass, and it does not meet the requirements of the dynamic damper.
More specifically described, in the dynamic damper whose metallic mass and the elastic support member are not bonded together by means of the adhesive, the metallic mass and the elastic support members are likely to be displaced relative to each other at an interface therebetween, upon application of a relatively large vibrational load to the dynamic damper, leading to an undesirably introduction of the air into the interface between the metallic mass member and the elastic support member, resulting in deterioration of a vibration damping effect. The similar problem, that is the undesirable introduction of the air into the interface between the metallic mass and the elastic support member, may possibly occur, when the dynamic damper is installed on the oscillating rod member and a primary load in its axial direction is applied thereto, and when the dynamic damper is installed on a propeller shaft of the automobile vehicle and small pieces of rocks or curb stones collide with the dynamic damper, for example.
It is therefor a first object of this invention to provide a dynamic damper which has novel structure wherein a metallic mass member has a relatively high-specific gravity and is constructed with a high-dimensional accuracy, and wherein the metallic mass member and an elastic support member are fastened to each other with high strength. The dynamic damper also permits a desired damping effect with high stability and a reduced manufacturing cost.
It is therefore a second object of this invention to provide a method suitable for producing the dynamic damper having such a novel structure indicated above.
The first object may be achieved according to a first aspect of this invention which provides a dynamic damper mounted on a rod-shaped oscillating member, comprising: (a) a generally cylindrical mass member disposed radially outwardly of the oscillating member and comprising a cylindrical metallic mass which is formed b forging and which is subjected to a scale-removal treatment; (b) an elastic support member for elastically supporting the cylindrical metallic mass for connection thereof with the oscillating member; and (c) an elastic covering layer adapted to cover a substantially entire area of a surface of the cylindrical metallic mass and integrally formed with the elastic support member, the elastic covering layer being fixed in close contact with the substantially entire area of the surface of the cylindrical metallic mass so that the elastic support member is firmly secured to the cylindrical metallic mass without using an adhesive.
In the dynamic damper constructed according to the first aspect of the invention, the use of the cylindrical mass member in the form of the forged cylindrical metallic mass permits a higher dimensional accuracy and a higher specific gravity of the mass member, in comparison with the case where the mass member is formed of a metallic material by casting. In particular, the cylindrical metallic mass formed by forging has the surface rugged by the scale removal treatment. Therefore, the elastic covering layer covering the rugged surface of the cylindrical metallic mass is firmly secured to the metallic mass owing to a mechanical bonding strength caused by an engagement of the rugged surface of the metallic mass and the inner surface of the elastic covering layer which is rugged corresponding to the rugged surface of the forged metallic mass upon vulcanization of a rubber material to form the elastic covering layer, resulting in eliminating the adhesive treatment. It is appreciated that the scale removal treatment is generally performed on forgings so as to remove scales formed on the surface of the forgings, so that no specific operation or facility for the removal of the scale is required, effectively avoiding a rise in the manufacturing cost.
In the dynamic damper constructed according to the first aspect of the present invention, the cylindrical metallic mass can be formed with a desired size and a desired mass, by effectively utilizing characteristics of the forgings. The dynamic damper also makes it possible to assure sufficient bonding strength between the cylindrical metallic mass and the elastic support member, without requiring the conventionally performed adhesive treatment with respect to the metallic mass and the elastic support member, lowering the manufacturing cost.
The cylindrical metallic mass may be formed of various kinds of metallic materials, and may preferably be formed of ferrous metals, such as carbon steel, and the like, in view of their characteristics such as a relatively low cost, formability and sufficiently high specific gravity. The cylindrical metallic mass may possibly have a polygonal shape other than the cylindrical shape in its transverse cross section. In order to obtain a further improved mechanical bonding strength between the metallic mass member and the elastic covering layer, the cylindrical metallic mass may further be formed with recesses and protrusions, cutouts and/or through holes, which are covered or filled with the elastic covering layer. Moreover, the metallic mass member may be tapered at its inner and outer circumferential surface, for improving an efficiency of the forging operation.
Further, the cylindrical metallic mass may be formed by a suitable forging method such as a cold forging and a warm forming. Preferably, the cylindrical metallic mass may be formed by a hot forging, in the light of the required working cost and an excellent productivity of the hot forging. After the cylindrical metallic mass is formed by the above indicated forging methods, the scale removal treatment is performed in order to remove the scale, i.e., a thin layer of oxide generated on the surface of the metallic mass during a period of cooling or annealing of the metallic mass. This scale removal treatment may suitably be performed by a shot blasting method using steel shots or cut wires, for example. The surface of the cylindrical metallic mass member is made roughed or rugged by the scale removal treatment so that the surface of the metallic mass preferably has a ten-point means roughness Rz in a range from 30 xcexcm to 200 xcexcm, more preferably from 50 xcexcm to 100 xcexcm. Namely an excessively small Rz value of the surface roughness of the metallic mass member leads to difficulty in obtaining a sufficient bonding stability between the metallic mass member and the elastic covering layer, while an excessively large Rz value of the surface roughness of the metallic mass requires the relatively long-time shot-blasting operation, leading to an increase in a manufacturing cost of the dynamic damper.
In addition, the elastic support member and the elastic covering layer which are integrally formed with each other, may be made of any one of various kinds of rubber materials or a mixture thereof. For instance, a rubber material such as NR, SBR or BR, or a mixture thereof may suitably be used. The elastic covering layer may require to cover only the substantially entire area of the surface of the cylindrical metallic mass, and does not necessarily require to cover local portions of the metallic mass to which supporting members of the mold are fixed for supporting and positioning the metallic mass in the mold. The thickness of the elastic covering layer is determined to be held preferably within a range of 0.5-5 mm, more preferably within a range of 1-3 mm, in view of the fact that the elastic covering layer having an excessively small thickness may deteriorate its durability or its bonding strength to the cylindrical metallic mass, while the excessively large thickness of the elastic covering layer may lead to an undesirably increase in the size of the dynamic damper.
In the dynamic damper constructed according to the present invention, the configuration and structure of the elastic support member are not particularly limited, but may suitably be determined taking into account the required vibration damping characteristics, so as to elastically support the cylindrical metallic mass with respect to the oscillating rod member. For instance, the elastic support member may comprise a pair of cylindrical connecting portions each extending axially outwards and radially inward from axially opposite sides of the metallic mass. These cylindrical connecting portions are adapted to elastically connect the metallic mass for connection thereof with the oscillating rod-member. The dynamic damper whose elastic support member constructed as described above makes it possible to reduce the ratio of its spring value as measured in the axial direction to its spring value as measured in the tortional or radial direction perpendicular to the axial direction, resulting in a reduction in the outside diameter of the dynamic damper.
Alternatively, the elastic support member comprises a central connecting portion extending radially inward from an axially intermediate portion of the metallic mass over an radial spacing between said cylindrical metallic mass and said oscillating member. This central connecting portion is adapted to elastically connect the cylindrical metallic mass for connection thereof with the oscillating rod member. The dynamic damper whose elastic support member including the central connecting portion makes it possible to increase the ratio of its spring value as measured in the torsional or axial direction to the spring value as measured in the radial direction perpendicular to the axial direction, resulting in a reduction in the axial length of the dynamic damper. It may be possible that the elastic support member comprises both of the pair of the cylindrical connecting portion and the central connecting portion.
The above-described second object of the invention may be attained according to a second aspect of the present invention which provides a method of producing a dynamic damper according to a first aspect of the invention, comprising the steps of: disposing the cylindrical metallic mass in a mold cavity of a mold for molding the elastic support member and the elastic covering layer; positioning the cylindrical metallic mass within the mold cavity such that the cylindrical metallic mass is supported at an outer circumferential surface thereof and at axially opposite end faces thereof with a plurality of supporting pins formed in respective portions of a molding surface defining the mold cavity so as to protrude into the mold cavity; pouring a rubber material into the mold cavity of the mold; and vulcanizing the rubber material filling the cavity for integrally forming the elastic support member and the elastic covering layer.
According to the above indicated method of the present invention, the cylindrical metallic mass can be positioned at a predetermined position within the mold cavity of the mold by means of the plurality of supporting pins such that the supporting pins are in contact with the respective portions of the circumferential surface and the axially opposite end faces of the cylindrical metallic mass with a reduced contact area, effectively reducing the area of the metallic mass member which is not covered by the elastic covering layer, ensuring an improved bonding strength of the metallic mass with respect to the elastic support member.
In the present method, the mold is required, for effectively supporting the: cylindrical metallic mass within the mold, to have at least three supporting pins which are in contact with the outer circumferential surface of the metallic mass and which are spaced apart from each other in the circumferential direction thereof, and at least two supporting pins which are in contact with the opposite end faces of the metallic mass, respectively. More specifically described, the mold may be constructed such that a plurality of supporting pins each preferably having a tapered shape, are independently disposed at respective portions so as to protrude into toward the circumferential surface of the metallic mass and axially opposite end faces of the metallic mass. Alternatively, the mold may be formed with at least three xe2x80x9cLxe2x80x9d shape supporting pins disposed in the peripheral portion of each of the respective axially opposite end portions of the mold cavity, such that the xe2x80x9cLxe2x80x9d shape supporting pins are spaced apart from each other in the circumferential direction and protrude radially and axially inward directions from the peripheral portion of the corresponding axially opposite end portion of the mold cavity. Thus, the xe2x80x9cLxe2x80x9d shape supporting pins are held in contact at their radially inwardly extending portions with the corresponding end face of the metallic mass, and at their axially inwardly extending portions with the circumferential surface of the metallic mass, thereby supporting and positioning the metallic mass within the mold cavity. In this case, each of the radially inwardly and axially inwardly extending portions of each xe2x80x9cLxe2x80x9d shape supporting pin preferably extends with a semi-circular shape in transverse cross section, in other words, has a ridged shape in its entirety.
With the metallic mass installed within the mold constructed as described above, a suitable rubber material is poured into the mold cavity and vulcanized so as to integrally form the elastic covering layer and the elastic support member. In this respect, the metallic mass does not need to be subjected to the adhesive treatment, but may be subjected to washing or degreasing treatments, as needed.